System and methods for extraction of threshold and mobility parameters in AMOLED displays

• US 8,599,191 B2
• Filed: 03/15/2013
• Issued: 12/03/2013
• Est. Priority Date: 05/20/2011
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Azizi, Yaser, Chaja, Gholamreza
• Primary Examiner(s): LEE, NICHOLAS J
• Application Number:
  US13/835,124
• Publication Number:
  US 20130201173A1
• Time in Patent Office: 263 Days
• Field of Search: None
• US Class Current: 345/212
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A system to improve the extraction of transistor and OLED parameters in an AMOLED display includes a pixel circuit having an organic light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input to provide the programming signal, and a storage device to store the programming signal. A charge-pump amplifier has a current input and a voltage output. The charge-pump amplifier includes an operational amplifier in negative feedback configuration. The feedback is provided by a capacitor connected between the output and the inverting input of the operational amplifier. A common-mode voltage source drives the non-inverting input of the operational amplifier. An electronic switch is coupled across the capacitor to reset the capacitor. A switch module including the input is coupled to the output of the pixel circuit and an output is coupled to the input of the charge-pump amplifier.

Claims

1. A data extraction system for an organic light emitting device (OLED) based display, the system comprising:

a pixel circuit including a drive transistor, an organic light emitting device, and a programming input coupled to the gate of the drive transistor, the drive transistor having a source or a drain coupled to the OLED;

a charge-pump amplifier having an input and an integrated voltage output;

a switch module including an input coupled to the output of the pixel circuit and an output coupled to the input of the charge-pump amplifier, the switch module including switches to steer current in and out of the pixel circuit, provide a discharge path between the pixel circuit and the charge-pump amplifier and isolate the charge-pump amplifier from the pixel circuit; and

a controller coupled to the pixel circuit, charge-pump amplifier and the switch module, the controller controlling voltage inputs to the pixel circuit, charge-pump amplifier and switch module in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including providing a program voltage to the programming input to either pre-charge a capacitance of the pixel circuit to a charge level and transfer the charge to the charge-pump amplifier via the switch module to generate the output voltage value, or provide a current from the pixel circuit to the charge-pump amplifier via the switch module to produce the output voltage value by integration;

a select transistor coupled between the programming input and the gate of the drive transistor; and

an output transistor having a source or drain coupled to the source or drain of the drive transistor, a source or drain coupled to said charge-pump amplifier, and a gate coupled to a read signal line.

2. The system of claim 1, wherein the charge-pump amplifier includes:

an operational amplifier having a negative input and a positive input coupled to a common mode voltage source;

a feedback capacitor coupled in a feed-back loop from the negative input to the output of the amplifier; and

wherein the output of the switch module is coupled to the negative input of the operational amplifier.

3. The system of claim 1 further comprising:

a select transistor coupled between the programming input and the gate of the drive transistor; and

an output transistor having a gate coupled between the source or drain of the drive transistor, and a source or drain coupled to the select transistor and a monitor output, the output transistor enabled via a select signal to the drive transistor and the select transistor.

4. The system of claim 1, wherein the drive transistor is an n-type transistor or a p-type transistor.

5. The system of claim 1, wherein the parameter is at least one of the threshold voltage and mobility of the drive transistor, the program voltage is set to a proper level to turn the drive transistor on, the switch module steers the current of the drive transistor into the charge-pump amplifier to be directly integrated for a certain amount of time, and the amplifier output is a value of at least one of the threshold voltage and mobility as a function of the amplifier'"'"'s feedback capacitor, length of integration time, and the program voltage.

6. The system of claim 1, wherein the parameter is the turn-on voltage of the OLED, the program voltage set to a proper level to operate the drive transistor as a switch, the switch module steers the current of the OLED into the charge-pump amplifier to be directly integrated for a certain amount of time, and the amplifier output is a value of the OLED'"'"'s turn-on voltage as function of the amplifier'"'"'s feedback capacitor, length of integration time, and the common-mode voltage set at the non-inverting input of the amplifier.